A B2B buyer sends a 500-unit order for sterling silver studs and asks why the factory is quoting 25 flask pours instead of one big pour. The buyer pictures a single tower of wax, poured once, done. The casting technician knows that a stud earring 18 mm tall will not sit inside a tree stacked 60 pieces high without half of them coming back as mis-runs. Piece count per cast is decided by geometry, not by how much wax you can glue to a base. Here is the working number we use on the bench.

Flask size sets the ceiling

We cast most production jobs in a 3-inch (75 mm) diameter, 8-inch (200 mm) tall flask. That flask holds about 1.4 liters of investment and is heated in a standard burnout oven. On that footprint a tree of studs or simple pendants tops out around 60 pieces for sterling silver. For 14k gold we drop to 45–50 because gold runs hotter and needs wider sprues. Large pieces — say a 25 mm signet ring — land at 12–18 per flask. Trying to force more pieces in means crowding the outer arms so close that metal cannot flow past the center, and the top third of the tree freezes short. The physics of tree building is covered in the lost-wax casting reference on Wikipedia.

Sprue diameter and feeders

The main sprue on a production tree runs 4–6 mm for silver and 5–7 mm for gold. Each branch to a piece is 1.5–2.5 mm. A stud earring needs a 1.5 mm branch; a ring shank needs 2.5 mm because it is a heavy mass that must feed as it solidifies. If we pack too many pieces on one main sprue, the feeder freezes before the parts and we get shrinkage porosity at the thickest point of every ring. We also leave 15–20 mm of clearance from the flask wall to the outermost piece so the investment does not crack on burnout. Our sprue layout rules are detailed in casting sprues and investment defects.

What actually lowers the count

Three things reduce piece count below the theoretical maximum. First, delicate pieces (thin bands, open filigree) get their own dedicated branch so they are not competing with a heavy bezel. Second, mixed metal orders — a buyer asking for silver bodies with gold accents — cannot share a tree, so we split the run. Third, first-article approval lots are always cast on a small 2-inch flask at 15–20 pieces so we do not risk 500 units on an unproven wax. The difference between a printed wax and a hand-carved one is described in lost-wax casting vs 3D-printed wax, and shrinkage allowance we build into the wax is covered in silver casting shrinkage tolerances.

Cost per piece on the tree

Flask cost breaks down the same way a print run does: one burnout cycle, one pour, one quench, and one divestment regardless of whether the tree holds 20 pieces or 60. The marginal cost of adding another branch is small — a few cents of wax and ten minutes of bench time — so pushing the tree from 40 to 58 pieces on a simple stud drops unit casting cost by roughly 30 percent. On a 500-piece reorder that is the difference between a US$1.20 cast and a US$0.85 cast. We rebalance the tree on every reorder once we know which pieces come back clean, because the safest tree for a first article is not the most efficient tree for the tenth.

How many studs fit on one 3-inch tree?

About 55–65 matched pairs (110–130 individual studs) when the earring head is under 8 mm. Bigger heads over 10 mm drop the count to 40 pairs.

Why can we not just stack more rows?

The top of the tree is the thinnest metal path. Above the 6th row, flow distance plus cooling time means the top arms freeze before metal arrives, producing mis-runs. We cap rows at five to six.

Does gold or silver change the count?

Gold needs wider sprues and longer cooling, so we cut roughly 20–25 percent more pieces from a silver tree for the same flask in 14k gold.

Can we mix ring sizes on one tree?

Yes, as long as the mass per piece is within plus/minus 2 grams. A 3 g band and a 12 g statement ring on the same tree will starve the heavy one. Porosity we see from bad feeding is diagnosed in 925 silver casting porosity defects.

Send us your piece weight and material for an exact piece-count quote. HOLYCOME runs wax printing, tree building, burnout, and casting under one roof — ask about our small-batch OEM program and send your STL plus target piece weight for a same-day flask count and price.

Frequently Asked Questions

How do I verify a factory before placing a bulk order?

Request a production video, business license, export records and a paid sample run. A factory that accepts a 50-piece test order is usually a real manufacturer.

What payment terms do you offer?

30% T/T deposit with the balance against the bill of lading. This protects both sides on first orders and can move to net terms after a track record.

What is your normal reject rate?

3–5% under 10x loupe inspection for cast and set pieces. Defective units are replaced free in the next shipment.

Where is the factory located?

Wuzhou, Guangxi, China—the core lab-grown and moissanite manufacturing cluster. Shipments go via Guangzhou or Shenzhen ports.